Off-highway trucks, such as those of the present invention, are typically used in quarries, steel mills, power plants, mines, and landfills. Off-highway trucks of this type can often carry or haul two hundred (200) to four hundred (400) ton plus payloads, which in truck body volume can translate from as much as one hundred sixty (160) cubic yards to three hundred twenty (320) cubic yards (and greater) in size. (To put this into perspective, a typical on-highway tandem axle dump truck is ten (10) cubic yards in size.) As such, the floors of the bodies on such off-highway trucks can easily be greater than sixteen (16) feet wide and often can exceed thirty (30) feet wide.
Off-highway trucks with carrying capacities of four hundred (400) tons or more are commonly used for hauling a variety of materials in various off road environments. As the generic name, “off-highway”, implies these vehicles are limited to off-highway, private road use and are typically used in mining environments. The typical norm for these off-highway vehicles is to operate on unpaved gravel or aggregate roads of varying quality. As mining operations in particular advance, new temporary roads are continually being constructed and old roads are abandoned. Thus, such ‘mine’ roads can be undulating and at times have extremely soft/poor under footing; causing the chassis of the off-highway trucks operating on these roads to twist and/or turn and at times rack their very frames along with the truck bodies sitting on the off-highway truck chassis.
The loading of these off-highway trucks, particularly with two hundred (200) to four hundred (400) ton plus payloads, needs to be carried out efficiently and quickly for the owners of such off-highway trucks to achieve the needed return on investment and payback on their off-highway trucks. A typical cost for these off-highway trucks is between twelve thousand ($12,000.00) and sixteen thousand ($16,000.00) dollars per ton of hauling capacity, such that a two hundred (200) ton hauling capacity off-highway truck might cost about $2,800,000.00 and a four hundred (400) ton capacity off-highway truck might cost about $5,600,000.00.
When one considers the costs for such off-highway trucks, the ‘hourly’ owning operating cost of such vehicles is in the ‘range’, for a two hundred (200) ton capacity truck, of about $220.00 per hour and, for a four hundred (400) ton truck, of about $380.00 per hour. Considering these owning—operating cost rates, it is ideal for these off-highway trucks to be operating and hauling as much material as possible each and every hour of operation. Consequently, at about $3.70 and $6.30 per operating minute, in the above examples, every minute that the trucks are not moving material comes at a real and quantifiable expense.
A typical off-highway truck haul cycle includes:                a. Loading,        b. Hauling the load to a dump point,        c. Dumping the load, and        d. Returning to a loading point for the next load.Typical complete haul cycles can be anywhere from fifteen (15) minutes to over sixty (60) minutes. The typical haul cycle is fifteen (15) to twenty (25) minutes. Assuming an average twenty (20) minute haul cycle, the loading of an off-highway truck should be quick and efficient, as every minute spent by an off-highway truck being loaded adds a minute to the total vehicle haul cycle.        
In typical off-highway truck high-production haulage operations the goal is to have a vehicle loaded in three (3) to four (4) minutes or less. Typical off-highway truck loading tools, whether they be large power shovels (either cable operated or hydraulic operated) or front end loaders, have a forty five (45) second to one (1) minute loading cycle. Thus by straight forward calculation to fill a four hundred (400) ton nominal capacity off-highway truck in three (3) to four (4) minutes will require four (4) to a maximum of five (5) shovel passes. For a nominal four hundred (400) ton capacity truck this means shovel or loader bucket capacities of at least eighty (80) to one hundred ten (110) tons per pass. Today, such shovel bucket capacities are achievable with loading shovels such as P&H 4100 or Caterpillar 7495 electric rope shovels.
With a loading shovel ‘bucket’ of a nominal one hundred (100) ton capacity to load a four hundred (400) ton capacity truck in a minimal amount of time, extremely significant truck body floor loading ‘impacts’ will occur as one hundred (100) ton plus buckets of material are repeatedly dropped on the truck body floor. These loading ‘impacts’ normally occur at or near the longitudinal center of the truck body floor. This area of the truck body floor, that is regularly load ‘impacted’ by material, can be referred to as the “sweet spot” of a truck body floor. Further, since off-highway truck bodies are normally “open ended” to facilitate the dumping out of hauled material, the truck body floor “sweet spot” typically extends along the center of the truck body floor from a short distance behind the truck body front wall rearward to a position slightly behind the off-highway truck chassis ‘dump body pivot’ or hinge connection.
The intensity of loading impacts on the truck body floor “sweet spot” is partially determined by the actual materials being loaded into and hauled by the off-highway truck body. For example:                1. Material such as plain alluvial dirt which rarely freezes into solid chunks (e.g., in more temperate climates) will cause relatively mild truck body floor impact        2. Material that has low tensile strength, such as coal that easily breaks up on impact, causes only mild truck body floor impact        3. Material that does break up relatively easy; but, contains little abrasive materials will be fairly easy on a truck body floor        4. Material that will break up when thrown against itself is only marginally harder on a truck body floor        5. Material that has high tensile strength and only breaks up in a mechanical crusher will impact a truck body floor life considerably more        6. Material that does not easily break up other than when mechanically crushed and that has highly abrasive qualities (such as having silica sand or quartz content) impacts the truck body floor “sweet spot” fairly extremely        
The floors of high-capacity off-highway truck bodies range in width from a nominal twenty (20) feet, up to and in excess of thirty (30) feet in width. With truck body floor structures of this width it is very important that the anchor and corresponding interconnections between the truck body floor and off-highway truck chassis are extremely substantial.
Rear dump, truck body floors typcially interface with an off-highway truck chassis at a minimum of at least four different points including:                1. the truck body to off-highway truck ‘dump chassis pivot’ or hinge point, that the truck body pivots about when dumping,        2. the truck body ‘frame rails’ which sit on the off-highway truck chassis and may be disposed on rubber frame pads between the body frame rails and off-highway truck chassis,        3. at the truck chassis hydraulic hoist, where body hydraulic dump cylinders connect to the truck body, and        4. some point near the front of the truck body via a chassis—body guide or stabilizer, that is disposed on the underside of the truck body floor and/or on the outside front wall of the truck body.        
Of these four points between the truck body to off-highway truck chassis interface, only the truck body to truck chassis ‘dump body pivot’ interfaces and constrains/retains the truck body on the off-highway truck chassis. As such, to keep a truck dump body from falling off of the off-highway truck chassis, tremendous dynamic loads in the truck body to chassis pivot area do occur in maintaining truck body stability on the off-highway truck chassis.
Such dynamic loads occur in normal off-highway truck operation, as the off-highway truck traverses undulating and curved off-highway truck haul roads. These dynamic forces can often be further exacerbated by a commonplace off center truck body loading condition. In fact, it is rare that in loading an off-highway truck body, the loads will be perfectly centered on the off-highway truck body/chassis.
On a typical two hundred forty (240) ton capacity off-highway truck with a truck body floor width approaching twenty five (25) feet the actual truck body pivots are only slightly more than five (5′ 3″) feet apart. Further, on a four hundred (400) ton capacity off-highway truck with a truck body floor width of around thirty (30) feet, the truck body pivots are only about seven and one half (7′ 6″) feet apart. Comparing an off-highway truck body floor width with the width of the truck body to chassis anchor point, it is relatively easy to recognize that significant cantilever stresses occur at the truck chassis to truck body anchor or pivot points, with these cantilever stresses being further amplified by any off center truck body load placement.
In fact, on a two hundred forty (240) ton capacity off-highway truck there is typically about ten (10) feet of body floor cantilevered on either side of the off-highway truck chassis body support, and on a four hundred (400) ton capacity off-highway truck there is often more than eleven (11) feet of body floor cantilevered to either side of the off-highway truck chassis body support. Of course, this cantilever effect is further multiplied by any off center load placement. Considering that the truck body center floor support area anchors these cantilevered truck body floor side areas on either side of the truck body center floor area, it is clear that the truck body center floor area must be able to withstand considerable load stresses.
Moreover, in the dumping of an off-highway truck body, it is the truck body center floor, where the off-highway truck chassis hydraulic dump cylinders are anchored. As such the “body floor sweet spot” is subjected to combined loading stress, extreme hauling stress and dumping stresses.
Other factors considered in the design and production of large off-highway truck bodies include the size of materials used to produce the truck body. For instance, the maximum width of most steel plate (as limited by steel mill production capabilities) is ten (10) feet, although there are a limited number of steel mills which can produce steel plate twelve (12) feet or more in width. However, to obtain the very high quality, high strength steel utilized in truck bodies ten (10) foot wide steel plate is a common limit. To further complicate the steel plate issue, the common steel strength for steel plate used in off-highway truck bodies is one hundred seventy five thousand (175,000) to two hundred thousand (200,000) pounds per square inch (psi) yield strength. However, the typical highest strength weld materials that can be used to join steel plates of the strength used in a truck body is eighty thousand (80,000) to one hundred (100,000) pounds per square inch yield. With these disparities in strength between the steel plates and the welds used to join them, it is desirable to minimize and wherever possible eliminate weld “butt” joints, and wherever possible for body structural members to be joined by overlapping or intertwining so that the inherent strength of the basic steel being used can be fully achieved.
In the design of off-highway truck bodies another important consideration is the transport of an assembled off-highway truck body. In today's world, transport of large over width loads can, at best, be a challenge and can sometimes be impossible. In the Eastern half of the United States of America, shipping anything wider than sixteen (16) feet in some areas is impossible. Even in areas where it can be done, the cost to ship structures of this width can approach $100.00 per mile of load movement. In contrast, in the Western United States of America, movement of over-width off-highway truck bodies (those over twenty (20) feet in width) can be done for $10.00 to $15.00 per mile. In other parts of the world, shipping width constraints may be smaller or larger than sixteen (16) feet wide, but rarely are shipping widths of twenty seven (27) to thirty (30) feet wide allowed without severe restrictions. In some cases this may mean that truck body component work must be initiated at one point, and completed truck body components then shipped to a fabrication point near the actual location of use, and the truck body then assembled at or near the final point of use. The degree to which the truck body components are assembled or completed at an initial point is typically dictated by the actual shipping constraints of the final delivery point of use.
There are several available options for truck body fabrication and shipping. These include:                1. full assembly and completion of a truck body at the initial point of fabrication, in which, due to shipping constraints, the typical overall truck body width may be limited to sixteen (16) feet,        2. initial truck body component assembly at a first point of fabrication, followed by shipment of truck body components (in kit form) to an intermediate finish point of fabrication for final assembly, and subsequent delivery to final delivery location, and        3. complete truck body component assembly at the initial original point of fabrication, shipment of fully fabricated truck body assemblies to an intermediate finish point of assembly, and subsequent delivery to final delivery location.Other options are available for fabricating and shipping truck bodies, but the above three options are the most common.        
To use an analogy from nature, the loadings and load distribution on an off-highway truck body floor can be compared with that of a “tree”. The trunk of a tree is like the center of an off-highway truck body, with the truck body floor supports extending outward off of the truck body center floor being much like the limbs of a tree. The roots of the tree are further analogous to the pivot connection point of the truck body to the off-highway truck chassis.
Today, in the off-highway truck operating arena it is commonly held that if a truck body floor lives a truck body lives. But, once an operator has to start working on and repairing a truck body floor, then that truck body floor and associated truck body components (body sides, body front wall, and body canopy) are close to the end of their useful life. Because of the high stresses that can and do occur in the area of the truck body to chassis pivot connection, when combined with the truck body floor “sweet spot” loading impacts, it is this area of the truck body to chassis interfaces, i.e., the truck body pivots, the truck body frame rails, and the truck hoist mounts that off-highway truck body floor failure normally begins.
In designing off-highway truck bodies, numerous factors should be taken into consideration, including:                1. the rocking and rolling stresses imparted on a truck body floor in the ‘dynamic’ operation of off-highway trucks that occurs when travelling over less than ideal ground or road support conditions,        2. the dumping of an off-highway truck body and the ‘dynamic’ stresses occurring in the area of the hydraulic dump cylinders and truck body floor attachment point as loaded truck bodies are raised and lowered,        3. the high cost of owning and operating an off-highway truck and the need to operate the off-highway truck and truck body at its maximum productive capabilities,        4. the need for off-highway truck fast ‘loading point’ turn around and loading-point bucket sizes that are 20 to 25% of an off-highway trucks carrying or hauling capacity,        5. the loading impacts (dependent on body application) on the body “sweet spot”,        6. the off-highway truck chassis to truck body connection stresses in the truck body “sweet spot” area,        7. the actual application in which the off-highway truck will be used, and the intensity of load impacting that can be expected to occur,        8. the critical nature of the off-highway truck chassis to truck body interface in conjunction with the amount of truck body floor that is cantilevered outside the pivot points between the off-highway truck chassis and truck body,        9. the availability of large-width steel plates and the need to overlap and/or intertwine body components wherever possible in the joining of different steel members, and        10. truck body shipping constraints from the initial point of off-highway truck body manufacture to a potential point of final truck body assembly, and then delivery to the ultimate off-highway truck body user.        
In considering all of the above truck body design criteria, it can be appreciated that the design and construction of the center of a truck body floor is crucial to the total success and longevity of large off-highway truck bodies. High structural loads can often occur in the off-highway truck body floor center chassis connection area. This area, in particular, of an off-highway truck body needs to be designed to withstand all the rigors that an off-highway truck body dump body pivot may be subjected to.